1. Technical Field
The present invention relates to environmental remediation technology, and more particularly, to a self-contained mobile vapor recovery apparatus and method for removing volatile materials from soil.
2. Related Art
Soil and water contamination due to spillage of hazardous chemicals and pollutants has long posed a serious problem. For instance, underground gasoline tanks may leak and discharge gasoline or other hydrocarbons directly into the ground. As another example, industrial solvents used in industrial processes may be illegally discharged into waste water or sumps, or inadvertently discharged directly into the ground. In any case, these materials, typically volatile organic compounds (VOCs), may propagate great distances through the ground and even enter ground water aquifers, thus resulting in a devastating environmental impact.
There are several conventional removal techniques which have previously been used in the art to remove volatile materials from the vadose earth layer. The vadose earth layer is the soil region just above the water table of the earth to the earth surface. The most common of these removal techniques is excavation in which all of the contaminated soil is physically removed and eventually replaced with fresh soil. While excavation is a relatively simple process, excavation is not practical when large volumes are involved due to prohibitive cost and time factors.
Another more sophisticated removal technique involves a circulation system for leaching volatile materials from the vadose earth layer into the water table, where the materials are recovered by a water removal well and pump system. The foregoing process is described generally in U.S. Pat. No. 4,167,973 to Forte et al. as well as many other patents, the Forte disclosure of which is incorporated herein by reference. Such processes are not always successful due to low water solubility of most common industrial pollutants, which results in lengthy and often costly recovery
Various vacuum removal techniques have also been used to extract volatile hazardous materials from the vadose earth layer. Vacuum removal techniques are often favored because they are less intrusive and destructive of the contaminated soil region to be cleaned up and, moreover, the volatile materials are retrieved in the form of material vapor within air, which is much more easily disposed of than materials contained within water or some other fluid. Conventional vacuum removal techniques are described in U.S. Pat. No. 5,116,515 to Selesnick, U.S. Pat. No. 5,111,883 to Savery, U.S. Pat. No. 5,050,676 to Hess et al., U.S. Pat. No. 5,076,360 to Morrow, U.S. Pat. No. 4,982,788 to Donnelly, U.S. Pat. No. 4,895,085 to Chips, U.S. Pat. No. 4,890,673 to Payne, U.S. Pat. No. 4,886,119 to Bernhardt et al., U.S. Pat. No. 4,730,672 to Payne, and U.S. Pat. No. 4,593,760 to Visser et al., all of the disclosures of which are incorporated herein by reference as if set forth in full hereinbelow.
Generally, the vacuum removal techniques involve situating one or more vertical withdrawal wells in the contaminated field. Each withdrawal well includes an elongated vertical borehole, into which there is placed a riser pipe. The riser pipe has numerous screened perforations or openings throughout its length and around its perimeter. Materials are vaporized and urged towards the vertical withdrawal well, through the screened openings, and upwardly toward the well head at the earth surface by generating a vacuum within the vertical withdrawal well. For this purpose, vacuum withdrawal equipment including a blower or other suction apparatus(es) is often situated at the earth surface near the well head. As materials are vaporized and pulled to the earth surface, the vaporized materials are collected and perhaps processed for disposal.
When materials are removed from the ground using vacuum removal techniques, air containing the material vapors is often discharged directly into the atmosphere, or discharged into the air after passing them through a catalytic converter. Federal, state, and local environmental pollution regulations place a limit on the amount of air pollutants which may be discharged in this manner. For example, a typical limit is 3.5 pounds (1.6 kilograms) per hour for volatile organic compounds. If a deep well is drilled, it is not uncommon for one withdrawal well alone to produce 2.5 pounds of solvent per hour discharged into the air.
The vacuum withdrawal equipment situated near the well head(s) is designed to remain in place for several years, because this length of time is usually needed to remove undesirable materials via the various vacuum removal techniques. Therefore, the vacuum withdrawal equipment is generally physically and permanently attached to the earth surface near the well head(s) and is protected in some manner from theft and/or adverse tampering. The vacuum equipment may include, for instance, a temperature gauge, a vacuum gauge, a flow measurement port, and/or a sample port. In this regard, see U.S. Pat. No. 5,017,289 to Ely, U.S. Pat. No. 4,890,673 to Payne, and U.S. Pat. No. 4,730,672 to Payne. Further, in many cases, the withdrawal wells are provided near the earth surface with a surrounding cement collar and a protective lid or cap, as illustrated in U.S. Pat. No. 5,076,360 to Morrow, U.S. Pat. No. 5,017,289 to Ely et al., and U.S. Pat. No. 5,050,676 to Hess et al. for security and safety reasons. The lid or cap is often locked.
A contaminated field may be provided with a plurality of withdrawal wells for removing unwanted materials because a plurality can tremendously accelerate the clean-up process. In this case, the withdrawal wells are usually channelled to a common manifold which leads to a single port for connection to a single blower or suction apparatus. Such a manifold arrangement is shown and described in, for example, U.S. Pat. No. 5,116,515 to Selesnick, 4,982,788 to Donnelly, and U.S. Pat. No. 4,895,085 to Chips (however, vapor and water extraction). A control unit is generally disposed for controlling suction in the common manifold and wells, material disposal, and/or other material processing systems.
The withdrawal wells are individually monitored by traveling to each well head in the contaminated field to observe the vacuum gauge and the sample port situated at each well head. Upon acquiring the foregoing data from the well heads, certain wells can be capped, while certain others are opened or are left open, so as to optimize material removal while abiding by the applicable environmental pollution regulations. In other words, it may be impermissible to draw from multiple wells to increase the speed at which the unwanted materials are removed from the soil because permissible environmental ambient air quality limitations would be exceeded. Accordingly, it is important to be able to monitor the quantity of vaporized materials being drawn from each well and its associated zone in the field.
Although successful to some extent, the conventional apparatuses and methodologies developed thus far for implementing vacuum removal techniques, especially with multiple withdrawal wells, are problematic and do not meet the present needs of the industry. First, the permanent installation of vacuum withdrawal equipment at a contaminated field poses many problems. The equipment generally involves piece-meal construction and cannot be easily installed. The equipment cannot be easily removed and moved after soil has been decontaminated or cleansed Moreover, the equipment is often damaged during removal, and the procedure is generally labor intensive. In addition, while the equipment is in operation, it is difficult and labor intensive to monitor the various zones of the contaminated field so as to efficiently dispense of the volatized materials while abiding by the applicable federal, state, and local environmental pollution regulations.